Conventionally, it has been known that, when a compressor is started under cooled conditions, a large amount of liquid refrigerant dissolves in a lubricating oil to make the lubricating oil dilute, giving rise to apprehension about the breakage of the compressor.
For the purpose of preventing the breakage of the compressor, it has been proposed to detect the voltage and current applied to the compressor to calculate the resistance of a motor winding of the compressor from the values of the voltage and current, and to calculate the current temperature of the compressor by utilizing the temperature characteristic of the resistance to preheat the compressor when the current temperature is not more than a predetermined temperature (See Japanese Patent Application Laid-Open No. 5-288411 (1993)).
Further, it has been proposed to cause restraint electrification (phase interruption electrification) of the winding of a motor for driving the compressor when the temperature of outside air is not more than a first set temperature at which there is a possibility that a refrigerant migrates in the compressor and when the temperature of a radiator for an inverter and the like is not more than a second set temperature at which the inverter is assumed not to be driven (See Japanese Patent Application Laid-Open No. 2000-292014).